I've been experimenting with microdata and thought I would try it on my blog. It turns out the template I was using already added some markup. It wasn't great and so I fixed up what I could.

To try and push my luck I have added more markup to my latest post but Google's Structured Data Testing Tool is unhappy about the itemprop='image' tags and I'm not sure why.

Results page.

It is my understanding, ignoring all the code in between, that I have structured the data thus:

<div itemscope='itemscope' itemtype='http://schema.org/BlogPosting'>
  <div itemprop='articleBody'>
    <a href="1.png" itemprop="url"><img itemprop="image sharedContent" src="1.png" /></a>
    <a href="2.png" itemprop="url"><img itemprop="image sharedContent" src="2.png" /></a>
    <a href="3.png" itemprop="url"><img itemprop="image sharedContent" src="3.png" /></a>
  </div>
</div>

And this looks correct to me. BlogPosting can have child elements articleBody and image according to https://schema.org/BlogPosting, but according to the SDTT:

The attribute itemtype has an invalid value.

Indeed, I have just tried the SDTT with the above example code and it is failing to validate.

So I'm obviously missing something. What am I doing wrong?